PROJECT ABSTRACT Emergency contraception (EC) provides a woman with an additional line of defense against unintended pregnancy following an act of unprotected intercourse. Orally-dosed EC works by delaying ovulation and reduces the risk of pregnancy for a single act of unprotected intercourse by 50-70%. Unfortunately, obese women are significantly more likely than their normal BMI counterparts to experience failure of orally-dosed EC and in some instances EC is equivalent to placebo. Our preliminary data provides evidence for testing a dose escalation strategy in an effort to provide improved efficacy from orally-dosed EC in obese women. We hypothesize that increasing the dose of orally-dosed EC agents will normalize the pharmacokinetics resulting in the expected treatment effect (delay in follicle rupture) in obese women. In this proposal, we plan to perform detailed pharmacokinetic and pharmacodynamic studies of ulipristal acetate- based EC in obese women and expand upon our preliminary findings of levonorgestrel-based EC.